The present invention relates, in general, to a computer controlled method of filling cylinders with gas and, more specifically, to a computer controlled method of filling cylinders with specialty gases requiring precise tolerance in obtaining desired gas mixture ratios.
For many years, the process of filling cylinders with gases or gas mixtures was performed manually. The gas distributor would have large storage cylinders filled with liquefied gases, such as oxygen, nitrogen, argon, carbon dioxide and helium. Via a manifold, he would simultaneously fill ten, twenty or more cylinders. As a first step, the cylinders were vented, meaning that whatever gas was in the cylinders was bled off. Usually a vacuum pumping system was connected to the manifold to draw a vacuum to evacuate the cylinders. Often one or more purges were performed, meaning, using a different pumping system, the cylinders would be filled with some of the compressed gas, which was then vented. Then, the cylinders were again evacuated. This purging cycle could be repeated as many times as was necessary with whichever gas was necessary to achieve the desired purity of the cylinders. Finally, the cylinders were filled with the specified gas or gas mixture to a predetermined pressure at a stated temperature.
In the process of making gas mixtures, two predominant methods existed. One method was to fill the cylinders with each gas to a different partial pressure to obtain the desired gas mixture ratios. The other method was to weigh in different amounts of various gases to obtain the desired gas ratios. In performing these various steps, the operator would monitor the temperature of the cylinders and the pressures in the system and, in some cases, a scale representing the weight of the gas in the cylinders. For example, when the cylinders were vented, the operator would monitor the pressure in the cylinders and when it reached a predetermined level, he would know it was time to start the evacuation process. Again, he would monitor the pressure to determine when the next step would be taken. The entire process was very time consuming and resulted in much lost time for the operator and the equipment.
It has been recognized that computer control of the filling process would substantially reduce the time it would take to vent, evacuate and fill cylinders, and thereby increase the number of cylinders that an operator could fill during a given time period. There are computerized systems in the marketplace. They are usually made for a particular system to fill cylinders with a particular gas or gas mixture and are not suited for high tolerance mixtures.
To meet this and other needs, and in view of its purposes, the present invention provides a method of filling a cylinder with a target weight of a gas. The method uses a computer controlled system that includes (a) a source of gas, (b) a plurality of valves for controlling flow of the gas to the cylinder, (c) a transducer for measuring pressure of the gas flowing to the cylinder, and (d) a weight scale for determining weight of the cylinder when filling the cylinder with the gas. The method of filling the cylinder with a target weight of the gas includes successively measuring the weight of the cylinder at periodic time intervals to obtain successive actual weights of the cylinder; opening a first valve and filling the cylinder with the gas at a high flow rate; and closing the first valve after reaching a predetermined weight difference between the target weight and an actual weight. After closing the first valve, the method opens a second valve and fills the cylinder with the gas at a low flow rate. After opening the second valve to fill the cylinder with the gas, the method also adjustably controls, via an adjustable valve, the flow of gas to the cylinder. The method differences each successively measured actual weight from the target weight of the gas to obtain multiple first difference values. The method also differences adjacently measured actual weights to obtain multiple second difference values. The flow of gas to the cylinder is adjustably controlled based on each first difference value and a corresponding second difference value.
It is understood that the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.